For the reduction of size (reduction in thickness) in, for example, a laminated ceramic capacitor, it is effective to reduce in layer thickness of not only the ceramic layers but also the internal electrodes. However, the reduction in the layer thickness of the internal electrodes makes it likely to cause electrode breakage during the firing step for sintering the raw laminated body. For preventing this electrode breakage, the following techniques, for example, have been proposed.
Japanese Patent Application Laid-Open No. 2008-226941 (Patent Document 1) prevents electrode breakage and achieves an electrode thickness of 0.8 to 1 μm by adopting a rate of temperature increase of 500° C./hour to 5000° C./hour in the firing step.
Japanese Patent Application Laid-Open No. 2000-216042 (Patent Document 2) prevents structural defects such as cracks in such a way that the reliability of a laminated ceramic capacitor obtained is enhanced, by adopting a rate of temperature increase of 500° C./hour or more in the 700° C. to 1100° C. range of the temperature increase process for firing, an oxygen partial pressure of 10−8 atm or less in the atmosphere at 1100° C. or more, and an oxygen partial pressure of 10−8 atm or more partially at 1100° C. or less in a temperature decrease process.
Korean Patent Application Laid-Open No. 10-2006-0135249 (Patent Document 3) achieves a balance between the prevention of electrode breakage and the prevention of overshooting the desired maximum firing temperature during a temperature increase by increasing the temperature up to the temperature 20° C. lower than the maximum temperature at a rate of 10° C./second.
While the effect of allowing reducing the layer thickness of the internal electrodes is achieved by means such as increasing the rate of temperature increase in the prior art described in any of Patent Documents 1 to 3 described above, the effect is limited, and for example, in a laminated ceramic capacitor including internal electrodes containing Ni as a conductive constituent, it is extremely difficult to achieve 0.3 μm or less as an electrode thickness after firing.
In addition, the atmosphere for firing a raw laminated body including internal electrodes using a base metal as a conductive constituent is, for example, a N2/H2/H2O system, and it is necessary to control the atmosphere to a more reducing side than the Ni/NiO balance oxygen partial pressure, which restricts the equipment and material design.
In addition, it is also effective to use a low-temperature sintered ceramic material in order to achieve the reduction in the layer thickness of the internal electrodes. The low-temperature sintered ceramic material may contain volatile constituents such as Li, and the volatile constituents tend to scatter during firing. Furthermore, the residual amount of the volatile constituents is likely to vary depending on the size of a raw laminated body to be fired, that is, the chip size, and the amount charged to the firing furnace, and it is difficult to suppress this variation in the residual amount.
Reduction in the thickness of the ceramic layers is also effective for reducing the size of the laminated ceramic capacitor as described above. However, the reduction in the thickness of the ceramic layers may lead to the following problems.
With the advance in reducing the thickness of the ceramic layers, the intensity of the direct-current electric field applied to the ceramic layers is further increased. In general, a ferroelectric ceramic is used for ceramic layers of a laminated ceramic capacitor with a relatively high capacitance per unit volume. However, the ferroelectric ceramic has the property that its dielectric constant is decreased when a large direct-current voltage is applied to it. Furthermore, the ferroelectric ceramic has a tendency to increase the rate of decrease in dielectric constant due to the application of the direct-current voltage when the dielectric constant is higher, and when the intensity of the direct-current electric field applied is higher.
The currently required reduction in the thickness of the ceramic layers has been advanced to result in an increase in the direct-current voltage per the thickness of the ceramic layer, thereby decreasing the dielectric constant of the dielectric ceramic at the direct-current voltage, and in return, decreasing the capacitance of the laminated ceramic capacitor at the direct-current voltage. More specifically, the reduction in the thickness of the ceramic layers has been already advanced to such an extent that it is difficult to achieve an increase in the capacitance of the laminated ceramic capacitor even if the reduction in the thickness of the ceramic layers is further advanced.
Accordingly, laminated ceramic capacitors have been desired which are less likely to decrease the dielectric constant of the dielectric ceramic, that is, superior in terms of DC bias characteristics, even when the intensity of the direct-current electric field applied is increased. For example, a technique described in Japanese Patent Application Laid-Open No. 2006-165259 (Patent Document 4) considers material compositions in order to improve the DC bias characteristics. However, in the case of changing the material compositions, it is difficult to achieve a balance with other characteristics (dielectric constant, temperature characteristics, reliability, etc.), leading to the problem of limiting the design flexibility.
It is to be noted that while the problems described above are associated with laminated ceramic capacitors, laminated ceramic electronic components other than laminated ceramic capacitors can also encounter the same problems.